Photo-sensitive device



Sept. 17, 1957 R. A. LANGEVIN 2,806,929

PHOTO-SENSITIVE DEVICE Filed April 16, 1954 INVENTOR R0559? 4.AAA/GEV/A/ ud} NM ITEM ATTO R N EYS United States Patent PHOTO-SENSITIVEDEVICE Robert A. Langevin, Wellesley, Mass., assignor, by mesneassignments, to Clevite Corporation, Cleveland, Ohio,

a corporation of Ohio Application April 16, 1954, Serial No. 423,571

4 Claims. (Cl. 201-63) This invention relates to a photo-sensitivedevice having particularly small dimensions, which is simple inconstruction, and which can be readily fabricated in large quantities atlow cost.

The various objects and advantages of the invention will be apparentfrom a consideration of the following description of a preferredembodiment of the invention considered in conjunction with theaccompanying drawings in which:

Figure 1 is a perspective view of a photo-sensitive device embodying theinvention; and

' Figure 2 is an enlarged perspective view showing the internalconstruction of the photo-sensitive device of Figure 1.

A small piece of single crystal germanium is prepared in the form of aminiature bar 2 which preferably is rectangular in cross-section, andwhich has a length at least three times its widest transverse dimension.The germanium should have an intrinsic resistance of at least 40 ohm-cm,under dark conditions, and preferably about 50 ohm-cm. The resistance ofsuch a piece of germanium is reduced when light strikes the surface ofthe bar.

This germanium bar 2 is embedded in a small cylindrical block 4oftransparent plastic material such as any of the well-known transparentor light-colored casting resins. The body of the plastic block 4preferably is cylindrical with one end dome-shaped as indicated atFigure 6. Ordinary gelatin capsules, such as are used for administeringmedicine, can be used conveniently as molds for supporting the resinduring the curing period.

The manner in which the electrical connections are made to the germaniumbar 2 is best shown in Figure 2. A lead wire 8 extends into the bluntend of the capsuleshaped plastic block 4 near the outer edge of theplastic and has a U-shaped end portion where it is soldered as at 10 toone end of the photo-sensitive bar 2. This same lead wire serves also asa mechanical support for the germanium bar 2, and for this purpose isprovided with the free-end portion 12 of the U which extends beyond theconnection 10 to a position near the outer edge of the plastic material4 and thence near the outer surface of the plastic block to form theU-shaped support.

The connection to the other end of the germanium bar 2 is made by meansof a lead 14 which extends into the blunt end of the plastic block 2near its outer edge, and passes Within the plastic material very nearthe 2,806,929 Patented Sept. 17, 1957 surface and also has U-shaped endportion which is soldered to the other end of the germanium bar asindicated at 16. This lead 14 also is utilized to assist in supportingthe photo-sensitive bar 2 by means of the free end 18 of the U whichextends beyond the connection 16 to a point'near the surface of theplastic block and then extends toward the blunt end of the plastic block4 near the outer surface of the plastic. The two connecting leads 8 and14 thus have generally U- shaped end portions with the germanium bar 2secured to the inner side of the base of the U of the lead 8 and to theouter side of the base of the U of the lead 14. The two U-shaped leadspreferably are rotated approximately from each other to provide maximumsupport during the molding operation.

This arrangement of the leads provides a convenient support for thephoto-sensitive bar 2 when the assembly of the leads 8 and 14 and thebar 2 are placed in the mold that is to receive the casting resin. Thiseliminates the necessity for providing any other means of positioningthe photo-sensitive bar 2 within the plastic material.

In addition, the auxiliary portions 12 and 18 on the leads serve toprovide a further support for the solder connections 10 and 16 after thecasting resin has set and to reduce the likelihood that internal strainswill break the solder connections.

The entire completed unit is small in size and is so 1 light in weightthat it can be supported entirely by the leads 8 and 14. The entire unitfor example may be no more than A in length and A" in diameter.

What is claimed is:

1. A photo-sensitive device comprising first and second connecting andsupporting leads having U-shaped end portions, an elongatedphoto-sensitive semi-conductive member connected between said leads atpoints a substantial distance from the ends thereof, and plasticsupporting means encasing said semi-conductive member and the U-shapedportions of said connecting and supporting leads.

2. A device as claimed in claim 1 wherein said semiconductive membercomprises a bar of germanium having a resistance, under dark conditions,of at least 40 ohmcm.

3. A device as claimed in claim 1 wherein said U- shaped portions ofsaid connecting and supporting leads are positioned approximately atright angles to each other.

4. A device as claimed in claim 1 wherein said plastic supporting meansis cylindrical in cross-section, and a significant portion of each ofsaid supporting leads extends adjacent the outer surface of said plasticsupporting means.

Burke Feb. 19, 1952 Ekstein Feb. 9, 1954

